A drive unit is disclosed by DE 198 41 159 A1. The drive unit is a compact unit mounted transverse in the motor vehicle and includes an electromotive drive and a transmission. In the drive unit, the output of the drive is transmitted via the transmission to two transmission output shafts of the drive unit. The transmission of the drive unit is formed by two sub-transmissions. A sub-transmission includes a rotating speed reduction stage, which involves a planetary drive. The second sub-transmission involves a differential. The input shaft of the planetary drive is a planet carrier that is connected with the rotor shaft of the electromotive drive rotating in the same direction. The rotation axis of the rotor shaft is supported on the central axis of the drive unit. The sun gear of the planetary drive is fixed at the housing of the drive unit. A set of planetary gears is meshing with the sun gear and a ring gear. The ring gear is the output shaft of the rotating speed reduction stage and is firmly connected with the cage of a differential. The cage and the ring gear can be rotated about the central axis of the drive unit. With the rotating speed reduction stage, first rotating speeds of the rotor shaft of the drive are reduced in second rotating speeds at the output shaft.
On the input side, the differential is provided with the differential cage, and on the output side with the transmission output shafts that can be rotated in relation to the rotor shaft. One of the transmission output shafts is coaxially guided through the hollow rotor shaft. The housing of the drive unit is divided in two chambers, one chamber housing the electromotive drive and the other the transmission.
Usually, gaps and other passages are formed between the different machine parts which are actively connected with one another or which are rotating in relation to one another. The gaps and passages must be sealed against any penetration of lubricating oil. Therefore, a radial shaft seal is arranged in an annular clearance in the drive unit, which annular clearance is located between the rotor shaft and the transmission output shaft. The radial shaft seal prevents lubricating oil transferring from the transmission chamber to the annular clearance. The heat generation of the electromotive drive can have the negative effect that the lubricating oil is coked.